I bought one a year or so ago and I don't know HOW I did anything without it! I adore my Polar HRM. The chest strap, for me, is totally non-existent when it's on.
I found that I actually work out HARDER knowing what I'm doing for sure, rather than guessing. I like seeing the number of calories I'm burning at the end of the workout, or looking at the little watch and seeing that I need to step it up! It helps me a ton.
I absolutely LOVE my HRM!! I have a polar FT80 and what's great is that you can customize it to your weight/height/sex and it will calculate how many calories to burn based on your activity level. I love knowing how many calories I'm burning while working out. Makes me work out that much harder.
And, with the FT80, you can upload your workouts to their website and also create workouts and use the HRM as a checklist to complete your workout. Highly recommend!!!
I just want to add too that I love my Polar. I have used one for years (well the years that I was a workout fiend, and yet again now). I really love it. It really helps you make sure you work out hard enough, but then again not too hard. I also love that it lets you know how many calories you have burned, and although I'm sure it is not 100% accurate, definitely more so than any treadmill or whatever else that estimates caloric burn. Highly recommended!
I have a Polar FT60 - love it. I like the soft strap that came with it, wearlink I think it is called? More comfortable than the hard plastic strap with I got with my Polar F6. The FT60 is programmable to gender, height, weight, etc as well. It has an OwnZone setting where you can set your own heart rate rate instead of using the standard. It also gives you access to the Polar website, which is fantastic. You can set training programs & goals there, too.
I have a TIMEX HRM and it works great. I think it cost about $60 on amazon. I also put in my age/weight/sex and it has a watch and a strap. It tells me how many calories I burn and is very encouraging. Just letting you know you may not need all of the bells and whistles of Polar. I've had mine since Jan and I love it.
My bf bought me a FT40 and I LOVEEEEE IT! I love being able to see how many calories I burn and like to push myself to burn a little more every workout. It really does help me pay attention to how hard im pushing myself. If you want one I say go for it. You wont regret it!